//重写toFixed方法
function toFixed(number, precision) {
    number = Math.round(+number + 'e' + precision) / Math.pow(10, precision) + '';
    let s = number.split('.');
    if ((s[1] || '').length < precision) {
        s[1] = s[1] || '';
        s[1] += new Array(precision - s[1].length).fill('0').join('');
    }
    return s.join('.');
}
